System and method for reduced power consumption and heat removal in optical and optoelectronic devices and subassemblies

ABSTRACT

A heat removal system for use in optical and optoelectronic devices and subassemblies is provided. The heat removal system lowers the power consumption of one or more active cooling components within the device or subassembly, such as a TEC, which is used to remove heat from heat generating components within the device or subassembly. For any particular application, the heat removal system more efficiently removes the heat from the active cooling component, by using a heat transfer assembly, such as a planar heat pipe type assembly. The heat transfer assembly employs properties like, but not limited to, phase transition change and thermal conductivity to move heat without external power. In some embodiments, the heat transfer assembly can be used to allow the active cooling component, such as a TEC to be removed, leaving the heat transfer assembly to remove the heat from the device or subassembly.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. application Ser. No.13/866,784, filed on Apr. 19, 2013, claiming priority to U.S.Provisional Application No. 61/635,694, filed on Apr. 19, 2012, theentire contents of which are incorporated herein by reference in theirentirety.

BACKGROUND

Data that is converted between optical and electrical formats whentransferred over fiber optics is typically accomplished by usingphotonic or optoelectronic devices that are contained in modules orsubassemblies such as a transceiver module. A transceiver moduletypically contains a laser transmitter circuit capable of convertingelectrical signals to optical signals, and an optical receiver capableof converting received optical signals to electrical signals. Thesemodules then interface with host devices such as line cards, routers,networks, host computers, switching hubs, etc., and there are manyapplications for transceiver modules ranging from fiber to the home,data centers, long haul and high-performance communications.

Transceivers may be manufactured in a form factor called a pluggable,and international industry standard have been adopted to defineparameters such as the physical size, shape, and power requirements ofthese transceivers. Examples include SFP (Small Form-factor Pluggable)transceivers, CFP (C Form-factor Pluggable), XFP (Small Form-factorPluggable) transceivers, and XFP+ (Enhanced Small Form-factor Pluggable)transceivers. Other transceivers can be built directly onto a circuitcard or onto a daughter card that plugs into a main circuit card. Withincreased data rates, smaller transceiver packages and the need tolocate very high capacities of fiber optic input/output on single linecards or low footprint switching boxes, the heat generation due tooptical transceivers has become a major problem. Heat generation andpower dissipation affect the performance and durability of thetransceiver and surrounding components and systems, if the heat is notdissipated from the transceiver to a standard temperature range via airflow or other efficient cooling mechanism for the line card and systemthat the transceiver is part of. Heat created by heat generatingcomponents of the transceiver, such as lasers, modulators, opticalamplifiers, receivers and associated electronics and thermal managementcomponents, is accordingly removed from devices by passive thermaldissipation or use of an active cooling device. However, the removal ofheat using traditional passive dissipation places limits on thetechnology in the transceiver, particularly the laser transmitter. Forhigh performance systems actively cooled devices increases thecomplexity and cost of the transceiver as well as the overall power andsize.

Further, optical subassemblies and internal devices like TransmitterOptical Subassemblies (TOSA), Receiver Optical Subassemblies (ROSA),photonic integrated circuits and associated driving, detecting, andcontrol circuitry generate heat and may require temperaturestabilization to meet the specifications for a certain communicationsenvironment and/or application. In addition, certain elements haveperformance and operating characteristics that are dependent on thedevice temperature, the ambient temperature range, and the requiredcooling from the device perspective and the system perspective. Thereare a variety of techniques to remove the heat from a device orcomponent that is actively cooled, for example forced air cooling,simple convection cooling, or thermoelectric cooling (TEC) and possiblyliquid cooling. For high performance transceivers, the amount of heat tobe removed requires active cooling which in itself significantly drivesup the power consumption and heat dissipation as well as the size ofthese components. Today, active cooling is typically accomplished usingan electrically active device like a thermo-electric cooler (TEC) of thephotonic circuits and/or other components that are not designed to beathermal or insensitive to temperature changes. Since many photoniccircuits and associated components are not athermal, especially withhigh performance specifications where data is transmitted and receivedon the fiber at distances greater than 10 kilometers and where fineoptical frequency spacing is employed as in dense wavelength divisionmultiplexing, new energy and costs efficient cooling techniques areneeded.

A disadvantage of active cooling, such as with a TEC, is that the TECitself requires power, generates heat and takes up space. The powerconsumed can be equal to or greater than that of the components whosetemperature is being stabilized. Typical TECs can require up to 3 W ormore power depending on the amount of heat that must be transferred froma device to an ambient temperature and the resulting amount of currentthat must be applied to the TEC to remove the generated heat.

Known prior art attempts to control the temperature of a laser in acommunication system include actively cooling the laser with athermoelectric cooler which is attached to a heat sink. Additional heatis removed from the heat sink using a heat pipe or other solid heattransfer device in a heat transfer relationship between a second heatsink. In other systems, heat pipes are used to cool a laser diode byproviding a thermally conductive path between a laser diode heat sinkand a thermoelectric cooler heat sink. Examples of such thermalsubsystems can be found in U.S. Pat. No. 6,285,476. Disadvantageously,however, these thermal subsystems dissipate heat through a complexsystem of multiple heat sinks interconnected with heat pipes or solidheat straps which are far removed from the heat generating component ofthe device, adding to the complexity and size of the device. Thesesystems also employ materials and designs that are not compact enough toform fit into today's optical transceivers or transceiver assemblies orsubassemblies, or they employ materials that oxide or corrode limitingthe performance lifetime (like copper), or materials that cannot bemachine using new micro-channel and nano-feature technologies thatsatisfy the requirements of heat removal from photonic oroptoelectronics devices and/or electronics used in conjunction withthese devices.

Therefore, it would be advantageous to develop and implement approaches,methods and apparatus that allow photonic, optical and optoelectronicdevices and components to be utilized in real world applications withoutthe use of an active cooling element like a TEC or reduce the amount ofwork, and therefore the power consumption required to drive the activecooling element under a set of given conditions. It would also beadvantageous if the components of the heat removal system are compact tofit into small footprint optical and optoelectronic devices andsubassemblies to meet the requirements of today's network devices andhave minimal amounts of interconnecting parts for ease of assembly. Itwould be further advantageous if the device and components can work inthe required temperature range for various applications, in particular,the laser and other optics that are housed in the TOSA, and other opticsand electronics in the ROSA whose functions are optimized by constanttemperature.

SUMMARY

According to the present invention, there is provided an apparatus thatemploys a heat transfer assembly, such as a substantial planar heat pipetype assembly or other equivalent passive thermal transfer technologythat removes heat more efficiently from heat sources in variousassemblies and subassemblies employed in the optical and optoelectronicarena.

According to one embodiment, a heat control system for use in an opticalor optoelectronic device or subassembly is provided. The heat controlsystem comprises a housing for containing the optical or optoelectronicdevice or subassembly and one or more heat generating components thatcan be optical or supporting electronic circuitry. An active coolingcomponent is positioned in thermal contact with the at least one of theheat generating components and a heat transfer assembly is positioned inthermal connection with the active cooling component. The heat transferassembly is preferably a substantially planar two dimensional vesselthat more preferably combines both thermal conductivity and phasetransition. In certain embodiments, the heat transfer assembly mayprovide a mechanical supporting structure a heat generating component.In some embodiments, the thermal connection between the active coolingcomponent and the heat transfer assembly may be a conductive platformwhich serves as the base of the housing. The heat generating componentmay be a laser, or may be a photonic integrated circuit or anoptoelectronic circuit. Preferably, the active cooling component is inthermal connectivity with the photonic integrated circuit or anoptoelectronic circuit, and the heat transfer assembly is in thermalconnection with the active cooling component. Using this invention,non-heat generating elements, like optical etalons, can have theirtemperature maintained for required performance and operation.

In a preferred embodiment, the heat transfer assembly extendssubstantially the width of the housing. In some preferred embodiments,the heat transfer assembly also extends beyond the surface area of theheat transfer assembly and a length of the heat transfer assembly isexposed at least in part externally to the housing. Also preferably, theheat transfer assembly is less than 1 mm in height, and extendssubstantially over the area of the active cooling component. In someembodiments, the heat transfer assembly is a substantially planar heatpipe type assembly comprising a two-dimensional vessel having interiornano-structures or micro-structures, which increase the interior surfacearea and heat transfer, i.e., cooling capacity of the heat transferassembly. Preferably, the substantially planar heat pipe type assemblycomprises interior nano-structures or micro-structures, more preferablythe substantially planar heat pipe type assembly andnano-structures/micro-structures comprise titanium.

In another embodiment, the device or subassembly comprises one or more,and preferably at least two heat generating components and at least oneor more active cooling component. The heat transfer assembly is inthermal connection with at least one or more of the active coolingcomponents. Preferably, the one or more heat generating components andactive cooling components are configured to stack vertically on top ofthe heat transfer assembly. In another embodiment, the conductiveplatform is disposed in between the heat transfer assembly and theactive cooling component and the heat transfer assembly is exposed atleast in part external to the housing.

In another embodiment, the heat transfer assembly is in direct thermalconnection and direct mechanical connection with the active heat removalelement. Preferably, the heat transfer assembly is in direct thermalconnection and direct mechanical connection with the active heat removalelement, and the active heat removal is in direct thermal connection anddirect mechanical connection with at least one of the heat generatingcomponents.

In other embodiments, the heat control system also has a heatdissipating apparatus, such as a fin, in thermal connection with theheat transfer assembly.

The heat control system may be used for heat control of a photonic oroptoelectronic circuit. In this embodiment, an active cooling componentis positioned in thermal connection with the photonic integrated circuitor optoelectronic circuit and the heat transfer assembly is positionedin thermal connection with the active cooling component. Optionally, aheat dissipating apparatus is positioned in thermal connection with theheat transfer assembly.

The heat control system may also be used in a transmitter opticalsubassembly. Preferably, the transmitter optical subassembly comprises apluggable transceiver or transceiver circuit embedded onto an electronicline card, daughter card or other portion of a system communicating witha fiber optic transmission channel or subsystem. According to thisembodiment, a circuit comprising a photonic integrated circuit oroptoelectronic circuit disposed within a transmitter optical subassemblyhousing. A thermoelectric cooler, or other active cooling device ispositioned in thermal connection with the circuit and a heat transferassembly, as described herein, is thermally connected to thethermoelectric cooler or other active cooling device. Preferably, thecircuit and thermoelectric cooler one are configured to stack verticallyon top of the heat transfer assembly and to fit within the housing.

In another embodiment of the invention, the active cooling element isomitted from all or a portion of the device or subassembly and the heattransfer assembly is positioned in direct thermal connection to the heatgenerating component. In a preferred embodiment, the heat control systemis used for heat control of a photonic or optoelectronic circuit. Inthis embodiment, a heat transfer assembly comprising a substantiallyplanar two dimensional vessel which combines both thermal conductivityand phase transition is positioned in direct thermal and mechanicalconnection with the photonic integrated circuit or optoelectroniccircuit. The heat transfer assembly may provide a mechanical supportingstructure for the photonic integrated circuit or optoelectronic circuit.The heat transfer assembly may also provide with the addition of theappropriate electrically insulating and conducting layers, electricalinterconnection between optical, photonic or optoelectronic circuit andcontrol and measurement elements including digital electronic circuits,logic and memory devices, RF electronic circuits, circuits that convertbetween analog and digital signals and temperature measurement elements,among other elements. Optionally, a heat dissipating apparatus ispositioned in thermal connection with the heat transfer assembly. In oneembodiment, components such as electronic circuitry, electronicinterconnects, insulting and conducting patterns, electronic circuits,electronic components, and sensing components, are mounted, i.e.,positioned in direct mechanical and/or direct electrical connection onthe heat transfer assembly to allow the heat transfer assembly to alsoserve as the electronic interconnect or circuit for the photonic oroptoelectronic devices and connected electronics and other devices.

FIGURES

These and other features, aspects and advantages of the presentinvention will become better understood from the following description,appended claims, and accompanying figures where:

FIG. 1 illustrates an exemplary prior art transceiver device;

FIG. 2 illustrates an exemplary prior art transceiver device having athermo-electric cooler (TEC);

FIG. 3 is a side view of an exemplary arrangement of a transmitteroptical subassembly showing the heat control system according to oneembodiment of the present invention;

FIG. 4 is a side view of an exemplary arrangement of a transmitteroptical subassembly showing the heat control system according to anotherembodiment of the present invention;

FIG. 5 is a perspective view of an exemplary arrangement of the heatcontrol system according to the present invention, showing a TEC inthermal connection with a heat transfer assembly and a circuit;

FIG. 6 is a perspective view of the exemplary heat control systempresented in FIG. 5, incorporated into an exemplary transmitter opticalsubassembly;

FIG. 7 is a perspective view of another exemplary arrangement of theheat control system according to the present invention, showing a TEC inthermal connection with a heat transfer assembly and a circuit; and

FIG. 8 is a perspective view of another exemplary arrangement of theheat control system according to the present invention, showing a heattransfer assembly in direct thermal connection to and a circuit and flexribbon.

DESCRIPTION

According to one embodiment of the present invention, there is provideda heat control system for use in optical and optoelectronic devices andsubassemblies including devices such as transceivers, transmitters andtransmitter assemblies, and other optical and optoelectronic devices andsubassemblies that benefit from heat removal and/or temperaturestabilization. The heat control system allows the optical andoptoelectronic subassemblies to operate at lower power consumptionthrough more efficient heat dissipation than known active heat removalsolutions. Further, the heat control system according to the presentinvention can be incorporated into devices and subassemblies with asmall footprint for use in small form factors.

More particularly, there is provided a pluggable transceiver ortransceiver circuit embedded onto an electronic line card, daughter cardor other portion of a system communicating with a fiber optictransmission channel or subsystem, which can support a broad variety ofoptical to electrical and electrical to optical conversion protocols fortelecommunications and data communications systems and applications.According to the present invention, a heat transfer assembly (alsoreferred to herein as a heat pipe) is incorporated into a transceiver,more preferably a pluggable transceiver, or a sub-module thereof, andthe heat transfer assembly is positioned in thermal connection to heatgeneration sources in optical devices and subassemblies that requireconstant temperature and/or heat removal.

As used herein, the term “heat transfer assembly” also referred toherein as a “heat pipe” or “heat pipe type assembly” comprises asubstantially planar two dimensional vessel which combines both thermalconductivity and phase transition. The heat transfer assembly is a heattransfer device having high thermal conductivity in a very smallfootprint, low profile, and fabricated from a material that can beconnected thermally to other materials. The heat transfer assembly canalso and can act as a substrate for metallization and mounting photonicand electronic circuits. The heat transfer assembly is a low profile(e.g., less than 1 mm) thermal ground plane that conducts heat throughthe heat pipe phase change mechanism. In some embodiments, the heattransfer assembly has internal structures, e.g., nano scale pillars thatform a very high surface area to facilitate heat exchange. The heattransfer assembly is distinguished from other thermally conductivebodies which are not planar and do not have the combined properties ofthermal conductivity and phase transition.

As used herein, the term “heat generating source(s)” or “heat generatingcomponent(s)” refers to devices and subassemblies which require removalof heat to stabilize the temperature for proper, optimal, or preferredoperation. The term also refers to other components which are passivenon-heat generating components or devices that benefit from heat removalor stabilization and/or whose temperature is maintained at a precisevalue in the presence of fluctuating ambient conditions, such as anetalon, for proper, optimal, or preferred operation. The term alsoencompasses the term devices or components to be cooled, as used herein.

In a one embodiment, the heat transfer assembly is positioned in thermalconnection with an active heat removal device like a TEC. Preferably,according to this embodiment, the heat transfer assembly is positionedin direct mechanical and direct thermal connection with the active heatremoval device without an intervening thermal subsystem, such as a heatsink. In another embodiment, the heat transfer assembly is positioned inthermal connectivity with the heat generation sources in the opticaldevices and subassemblies without a TEC. Preferably, according to thisembodiment, the heat transfer assembly is positioned in directmechanical and direct thermal connection with the heat generationsource.

Temperature stabilization and heat removal in optical and optoelectronicdevices and subassemblies may be accomplished using an active heatremoval device such as a thermo-electric cooler (TEC). A TEC is a devicethat uses the Peltier effect to create a heat flux between the junctionof two different types of materials when current is passed through thedevice. When electrical power is supplied to the TEC, one side of theTEC generates heat and the other side is cooled. When cooling a heatgenerating component or device, the heat generating component is mountedto the heat absorbing side of the TEC and the other side of the TEC,i.e., the heat rejecting side, is connected to a thermal ground, orconductor, or is cooled with airflow or other heat dissipation method.

The heat control system according to the present invention reduces thethermal impedance between the device to be cooled and the eventual heatremoval mechanism. The devices to be cooled include photonic,optoelectronic and electronic heat sources as well as supportingelectronic circuitry, electronic elements and other measurement andcontrol devices. The heat control system of the invention minimizes thethermal impedance between the heat sources and heat removal elementswhile also providing a platform to form electrical interconnections, anelectric ground plane or planes, a thermal ground plane and/or amechanical supporting structure. These features of the heat controlsystem have been found to be highly advantageous in building energyefficient, low power, compact and reliable optical communicationscomponents.

According to one embodiment of the present invention, the heat controlsystem works with known active heat removal devices, such as a TEC, tolower the power consumption of the active heat removal device used inoptical and optoelectronic devices and subassemblies. In otherembodiments, the heat control system operates directly with the heatgenerating components of the optical and optoelectronic devices andsubassemblies to lower power consumption without the use of an activeheat removal device, such as a TEC.

The advantages of the heat control system according to the presentinvention include, reduced power consumption for compact optical andoptoelectronic devices and subassemblies, a smaller footprint, lowercost, and broader applications for optical, integrated optic andoptoelectronic technologies. Further, the heat control system accordingto the present invention is capable of meeting the needs of today's WDMnetworks including lower cost and lower power consumption transceivers,particularly pluggable transceivers. Transceivers and accompanyingcomponents for today's WDM networks must operate over a required ambienttemperature range, for example −20 to +100 degrees Fahrenheit (+20 to+50 degrees Celsius), for data centers or wider temperature ranges fortelecommunications or other applications. However, the laser and otheroptics and electronics that are housed in the TOSA, and other optics andelectronics in the ROSA, and other portions of the transceiver, are heldto a more constant temperature in order to function. This isparticularly true of the laser and other optic components like aFabry-Perot etalon, a well-known and widely used device for locking thelaser output to a desired wavelength or optical frequency. Certaincomponents, like the laser, require removal of heat to stabilize thetemperature and to fix the laser output properties. Other componentslike the etalon are passive devices whose temperature must be maintainedat a precise value in the presence of fluctuating ambient conditions.

The heat control system according to the present invention is capable oflowering power consumption while at the same time effectively andefficiently providing heat removal/cooling in a cost effective manner.In addition, the heat control system is capable of being implementedinto a variety of optical devices and optoelectronic devices, meaningdevices having both optical and electrical components, such astransponders, transceivers, transmitters, and/or receivers and a varietyof form factors including SFP, CFP, XFP, and XFP+ conforming devices forimplementation into today's WDM networks, and other systems includingvarious telecommunications networks, local area networks, metro areanetworks, storage networks, wide area networks and the like. However,the present invention is not limited to pluggable transceiver formfactors and can be used for transceivers built directly onto circuitcards, daughter cards or other subassemblies. It will be appreciatedthat the devices and systems according to the present invention need notcomply with standardized form factor requirements and the principles ofthe present invention are adaptable to a variety of sizes andconfigurations according to various design parameters. Further, the heatcontrol system according to the present invention is adaptable for usein devices which are suitable for many data rates including but notlimited to 1 Gigabit per second, 2 Gigabit per second, 4 Gigabit persecond, 10 Gigabit per second and higher bandwidth fiber channels.

Further, the heat control system according to the present invention isimportant to the use of optical and optoelectronic devices andsubassemblies in communications applications. As the performance andfunctionality of optoelectronic devices and subassemblies, in particularthe TOSA, ROSA and pluggables, increases, and their size decreases, itbecomes increasingly important that excess heat generation is removedefficiently and without consuming unneeded excess power. Removal of theactive cooling element, such as the TEC, all together, or reducing theamount of work it does is accordingly an important technologicalinnovation.

The heat control system minimizes thermal impedance between the heatsources and heat removal elements and at the same time can provide aplatform to form electrical interconnections, an electric ground planeor planes, a thermal ground plane and/or a mechanical supportingstructure. Accordingly, the heat control system according to the presentinvention is capable of being implemented into a highly compact formwith superior performance.

Referring now to FIG. 1, an example of a prior art transceiver 100 isshown. Prior art transceivers 100, as illustrated in FIG. 1, incorporatea transmitter optical subassembly (TOSA) 102 or optical transmitterequivalent circuit or subassembly and a receiver optical sub-assembly(ROSA) 104 or optical receiver equivalent circuit or subassembly as wellas various analog and digital electronics for modulation, clock and datarecovery, and control 106, 108, and 110 that communicate with the TOSAand ROSA as well as control other information and functions within thetransceiver 100 and outside the transceiver 100, such as data and clock112, control and monitoring 114, and other outside electronics 114 thatsit outside the transceiver 100 or in other embodiments may be containedall or partially inside the transceiver depending on the application andarchitecture. The transmitter 100, includes optics (not shown), such asa laser (12) that are in the TOSA 102 or equivalent and optics, such asa photodetector (not shown) are housed in the ROSA 104 or itsequivalent. The transmitter 102, part of the transceiver 100, usesoptics that launch a transmitted optical signal 118 onto the fiber (notshown). The receiver 104 part of the transceiver 100 uses optics toreceive a received optical signal 120, which is then converted andtransmitted as an electrical signal by the transceiver 100. For low-costapplications, ultra low cost lasers (not shown) operating at 850 nm or1310 nm with the capability to transmit over short distances are used(e.g. 100 m to 2 km). In some designs, these, or other lasers arecooled, while in other designs, the lasers can be operated as uncooled.For higher performance fiber transmission optics operating in the 1550nm window, or when surrounding wavelength windows are employed,temperature plays a more critical factor.

Referring now to FIG. 2, an exemplary prior art transceiver assembly isillustrated. In FIG. 2, a prior art transceiver assembly 200, having athermo-electric cooler (TEC) 202, which is used as an active componentto removed heat generated from heat generating devices is shown. Thetransceiver 200 comprises one or more heat generating components, suchas a laser/transmitter 204 and/or passive components that do notgenerate heat but require temperature stabilization such as the etalon206 as well as other components 208, 210, 212 of the transceiver 200,which rest on a platform 214, a platform that is typically made of agood thermally conducting material that is also thermally stable and hasother desirable properties to manufacture such components. Intransceiver 200 devices, such as shown in FIG. 2, heat generatingdevices like a laser/transmitter 202 are in thermal communication withthe TEC 202, which transfers heat to the outside of the transceiver 200,through a thermally conductive plate, which is then cooled by active airflow, convection or other heat transfer process. In prior art devices,the TEC 202 is also used to set the operating temperature and hence thecavity length of the etalon 206. The TEC 200 itself, depending on thetemperature difference between the top side of the TEC 216, which is theside adjacent to the component to be cooled or to be maintained at atemperature, and the bottom side of the TEC 218, which is the heatrejecting side, located at the far side from the component to be cooledand consumes a certain amount of power. For a given heat load on theheat removal side, more power is required to cool the heat removal sideas the temperature increases and as the temperature difference betweenthe heat generation and heat removal side increases.

Other approaches to reduced power consumption involve designing theactual devices and components so that they can be operated over a givenambient environmental temperature range and the properties of the devicedo not change or are robust to over this fluctuation, called a-thermaldesigns. However, there are wide ranges of passive and active devicesthat cannot today be made a-thermal (insensitive to a range oftemperature changes). Other approaches utilize solid materials such ascopper, or materials fabricated with increased surface area such as heatsinks, to remove heat. However, these materials and structures are nothighly efficient at removing heat in these applications and environmentswhen employed on their own.

According to the present invention, a heat removal system has been foundthat more efficiently removes heat from a heat source or heat generatingcomponents in an optical or optoelectronic device or subassembly tosignificantly reduce the power consumption in the optical oroptoelectronic device or subassembly. Transceivers, transmitters andtransmitter assemblies, and other optical and optoelectronic devices andsubassemblies are provided that have reduced power consumption and/orenhanced temperature control and/or temperature stability within thedevice or subassembly. These devices and subassemblies have heatgenerating components and either require heat removal or temperaturestabilization. The heat removal system according to the presentinvention allows these devices and subassemblies to operate at lowerpower consumption and heat dissipation than those that use other activecooling devices, such as a TEC, alone and/or other active heat removalsolutions.

As will be understood by those of skill in the art, the heat removalsystem, devices and subassemblies according to the present invention,lowers the power consumption of the active cooling component, such as aTEC. For any particular application, the heat removal system moreefficiently removes the heat from the TEC, by using a heat-pipe typeheat transfer assembly. The heat-pipe heat removal system employsproperties like, but not limited to, phase transition change to moveheat without external power. In some embodiments, the heat-pipe heatremoval system can be used to allow the active cooling component, suchas the TEC, to be removed all together, leaving the heat transferassembly to remove the heat from the device or subassembly. In additionto removing heat from heat generating components such as photonic oroptoelectronic circuits, other co-located electronic circuits that arepackaged with or near the photonics or optoelectronics can also have theheat removed by the heat removal system according to the invention.

Referring now to FIG. 3, a side view of an exemplary arrangement of adevice 300, such a transmitter optical subassembly, is shown. The device300 employs the heat control system according to one embodiment of thepresent invention. As shown in FIG. 3, the device 300 has one or moreheat generating components, such as a laser/transmitter 302 or a passivenon-heat generating component like an etalon 304. The heat controlsystem comprises one or more active cooling components, 306, 308 such asthermo-electric coolers, which are in thermal connection with the heatgenerating components 302, 304. A heat transfer assembly 310, such as aheat pipe type assembly, is positioned in thermal connectivity with theone or more active cooling components 306, 308. The active coolingcomponent 306, 308 is preferably in thermal connection with a heatconducting material, and heat is transferred from the active coolingcomponent 306, 308, through the heat conducting material and then to theheat transfer assembly 310.

As shown in FIG. 3, in one embodiment, the bottom plate 312 of thehousing 314 of the device 300, serves as a heat conducting material totransfer heat from the active cooling component 306, 308, to the heattransfer assembly 310. The TEC bottom plate 316, or heat rejecting sideof the TEC, is in thermal connectivity with the bottom plate 312 of thehousing 314. For example, when the device 300 is a transmitter opticalsubassembly (TOSA) or receiver optical subassembly (ROSA) or otheroptical package, the bottom plate 312 of the TOSA or ROSA housing 314,is the bottom of the optical package where the maximum heat istransferred from the heat rejecting side of the TEC. The bottom plate312 is mounted directly to the heat removal element 310, e.g., a heatpipe, or equivalent passive assembly using a low thermal impedancebonding material.

In each stage that connects the heat generating region or regions on theheat generating component(s), such as photonic circuit or supportingelectrical circuits, it is preferable to keep a minimum thermalresistance path between the heat removal elements 306, 308, and the heattransfer assembly 310, such as a heat pipe. As shown in FIG. 3, usingthe heat transfer assembly, such as heat pipe technology, the heatdifferential from the heat pipe hot side to the heat pipe cold side tothe ambient air is transferred more effectively by using the passivedevice. The heat transfer assembly 310 in general might use a principlelike a phase change of a liquid or other material to transfer heat fromthe hot side 320 (in thermal connectivity with heat rejecting side ofthe TEC (316)) to the cold side 322 of the heat transfer assembly 310.The heat transfer assembly 310 uses air flow or other methods to createa heat differential or gradient in the element 310. The use of a phasechange process allows the element 310 to perform work on removing theheat from the TEC 306 without external power, as it is a closed system.This removal of heat from the TEC 306 allows the TEC 306 to be run at alower current, thereby reducing the power consumption of the TEC 306,and overall power consumption of the device 300.

According another embodiment of the invention, one or more of the activecooling elements of an optical or optoelectronic device or subassemblyis omitted from the device or subassembly and the heat transfer assemblyis positioned in direct thermal connectivity with a heat generatingcomponent, such as a laser, or etalon or other heat generatingcircuitry. In this embodiment, one or more heat generating components ispositioned in a direct thermal connection to the heat transfer assembly,thereby eliminating the power consumption, space and cost of the activecooling component, such as a TEC, altogether. The removal of the activecooling component also significantly reduces the power consumption ofthe device, yet the heat transfer assembly still maintains a suitabletemperature controlled environment within the device or subassembly.

Referring now to FIG. 4, a side view of an exemplary arrangement of adevice 400, such a transmitter optical subassembly, according to anotherembodiment of the invention, is shown. The device 400 employs the heatcontrol system of the invention in another configuration of an opticalor optoelectronic device or subassembly to lower the power consumptionof the device, yet still maintain suitable temperature control of theheat generating components of the device. As shown in FIG. 4, the device400 has first heat generating component(s) 402, such as a laser and/orother electronics, which are in thermal connection to a heat transferassembly 404. In this embodiment, the device 400 may have second heatgenerating component(s) 406, such as an etalon or other electricalcomponents, which are in thermal connection with an active coolingcomponents, 408, such as a thermo-electric cooler. The heat transferassembly 404, such as a heat pipe, is positioned in thermal connectivitywith the first heat generating component 404 and the active coolingcomponent is omitted from this portion of the device 400 such that thepassive heat control element 404 is the primary heat removal mechanismfor the thermally connected first heat generating components 404. Theheat transfer assembly 404 is positioned between the first heatgenerating component 402 and the bottom plate 410 of the housing 412 ofthe device 400. The bottom plate 414 of the active cooling component 408is in thermal connectivity with the bottom plate 410 of the housing 412and the top plate 418 of the active cooling component 408 is in thermalconnectivity with the second heat generating component(s) 406. Thebottom plate 410 of the device 400 serves as a heat conducting materialto transfer heat from the active cooling component 408 to the heattransfer assembly 404, thus dissipating heat from the second heatgenerating component 406 through the active cooling component 408 andlowering the power consumption of the device 400. In this manner, theheat transfer assembly 404 removes heat from both the first and secondheat generating components 402, 406.

According to this embodiment, when the device 400 is a transmitteroptical subassembly (TOSA) or receiver optical subassembly (ROSA) orother optical package, the bottom plate 410 of the TOSA or ROSA housing412, is the bottom of the optical package where the maximum heat istransferred from the heat rejecting side of the TEC. The bottom plate410 is mounted directly to the bottom side 414 of the active heatremoval component 406 and also to the bottom side 416 of the heattransfer assembly 404 e.g., a heat pipe, or equivalent passive assemblyusing a low thermal impedance bonding material. The top side 418 of theheat transfer assembly 404 is also in thermal connection to the firstheat generating component 402. Thus, the passive heat removal component404 dissipates heat from both the first heat generating component 402and the second heat generating component 406, through the heat transferassembly 404.

As described above in reference to FIG. 4, in each stage that connectsthe heat generating region or regions on the first and second heatgenerating component(s), such as photonic circuit or supportingelectrical circuits, it is preferable to keep a minimum thermalresistance path between the heat removal elements and the heat transferassembly 404. As shown in FIG. 4, using the heat transfer assembly, theheat differential from the hot side to the cold side to the ambient airis transferred more effectively by using the passive device 404. Theheat transfer assembly 404 may use a phase change of a liquid or othermaterial to transfer heat and the heat transfer assembly 404 uses airflow or other methods to create a heat differential or gradient in theelement 404. The use of a phase change process allows the element 404 toperform work on removing the heat from the TEC 306 without externalpower and also remove heat from the heat generating elements 402 whichare not cooled with an active cooling device. This removal of heat withthe passive element 404 allows for removal of one or more active coolingelements, and allows the TEC 408 to be run at a lower current, therebyreducing the power consumption of the TEC 408, and overall powerconsumption of the device 400.

Referring now to FIGS. 5 through 8, other embodiments of the heatcontrol system according to the present invention are shown, with likenumbers referring to like elements. As shown in FIGS. 5-8, the passiveheat control element can be incorporated with increasing levels ofmechanical, thermal and electronic integration, where each improvementof integration is designed to remove thermal impedance, simplifymanufacturing, reduce size and reduce overall power consumption andreduce cost and complexity of manufacturing as well as improvereliability.

Referring again to FIG. 5, a perspective view of another embodiment ofthe heat control system according to the present invention is shown.FIG. 5 shows a heat control system 500 for use in the heat control of aphotonic or optoelectronic circuit. The heat control system 500comprises a photonic integrated circuit or optoelectronic circuit 502which is positioned in thermal connectivity to an active coolingcomponent 504, which in a preferred embodiment is a thermoelectriccooler (TEC). The TEC 504 is then thermally connected to the heattransfer assembly 506. As the TEC 504, is in thermal connection to thecircuit 502, and also in thermal connection to the heat transferassembly 506, the heat transfer assembly 506, dissipates heat from theTEC 504 and the circuit 502. As also shown in FIG. 5, the heat transferassembly 506, may be thermally connected to the TEC 504 through aconductive platform 508, which is disposed in between the heat transferassembly 506 and the active cooling component (TEC) 504. In someembodiments, when the system is incorporated into a housing, the heattransfer assembly 506 is exposed at least in part externally to thehousing. Preferably, the heat transfer assembly 506 extendssubstantially the width of the circuit 502 and a length of the heattransfer assembly is exposed at least in part externally to the housing(not shown). As also shown in FIG. 5, the heat transfer assembly 506provides a mechanical supporting structure for the heat generatingcomponent 502 and the active cooling component 504. The heat transferassembly 506 also can provide a platform for forming electricalinterconnections, an electrical ground plane or planes and a thermalground plane. More preferably, in the heat control system 500, the heatgenerating components 502 and active cooling components 504 areconfigured to stack vertically on top of the heat transfer assembly 506,such that the system 500 can be sized to fit within various standardform factors as described herein and also future form factors. The heattransfer assembly is preferably less than 1 mm in height, and extendssubstantially over the area of the active cooling component and canserve as a mechanical supporting structure for the assembly. Preferably,the heat transfer assembly is in direct thermal connection and directmechanical connection with the active heat removal element, and theactive heat removal is in direct thermal connection and directmechanical connection with at least one of the heat generatingcomponents. As also shown in FIG. 5, the heat control system may alsohave a heat dissipating apparatus 510 in thermal connection with theheat transfer assembly 506. The heat dissipating apparatus 510 may be afin assembly, as shown in FIG. 5, or another similarly operating devicewhich serves to radiate heat out of the heat transfer assembly 506.

Preferably, according to this embodiment, the photonic or optoelectroniccircuit 502 and/or other electronic components and circuits are mounteddirectly to an electronic interconnect and deposited directly onto theheat absorbing side of the TEC 504. Also preferably, the photonicintegrated circuit or optoelectronic circuit 502 is positioned on aribbon 512, or flex circuit, mounted on a flexible substrate, such aspolyimide, PEEK, or a transparent conductive polyester substrate. Theribbon 512 or other electronic interconnect is directly attached totraces patterned on the TEC 504. The TEC 504 is then connected to thethermal removal stackup and heat transfer assembly 506 as shown in FIG.5. However, other embodiments are within the scope of the invention, aswill be understood by those of skill in the art with reference to thisdisclosure.

Referring now to FIG. 6, a perspective view of the embodiment of theheat control system shown in FIG. 5, incorporated into an exemplarytransmitter optical subassembly 600 is shown. As shown in FIG. 6, thetransmitter optical subassembly 600 comprises a housing 602 that formsan interior space for housing the components, such as focusing andcollimating lenses 604 and 606, respectively. The transmitter opticalsubassembly 600 is preferably tunable and overall of a small size foruse in an optical transceiver or other small sized application. Thehousing 602 has a generally rectangular body with exterior walls 608 anda bottom 610 and a top 612. An optical ring assembly, or interface 614extends outward from the housing 602. Positioned at least partiallywithin the housing 602 is the photonic integrated circuit 502 and heatcontrol system shown in FIG. 5. The photonic integrated circuit 502 ispositioned at least partially within the housing 602. The heatgenerating components 502 (including the photonic integrated circuit)and active cooling components 504 are configured to stack vertically ontop of the heat transfer assembly 506. The heat transfer assembly 506 isthermally connected to the TEC 504 through a conductive platform 508,which is disposed in between the heat transfer assembly 506 and theactive cooling component (TEC) 504. The heat transfer assembly 506 ispositioned exterior to the bottom 610 of the housing 602, and in thermalconnection to the TEC 504. The heat transfer assembly 506 extendssubstantially the width of the housing 602 and extends beyond the lengthof the housing 602. As also shown in FIG. 6, the heat control system 500has a heat dissipating apparatus 510 in thermal connection with the heattransfer assembly 506 to radiate heat out of the heat transfer assembly506.

In a preferred embodiment, the photonic or optoelectronic circuit 502 ismounted to a carrier such as silicon nitride along with other electroniccomponents or circuits including but not limited to a thermistor,termination resistors and capacitors, inductors, modulator or laserdriver circuits, transimpedance amplifiers (TIAs). The DC and RF signalsthat communicate with the photonic or optoelectronic circuit 502 orother electronic components and circuits are routed via a flex ribboncable 512 or circuit card that may or may not extend all the way to thephotonic or optoelectronic circuit, and wire bonds, bump bonds or otherelectrical connection mechanism is used to connect to the photonic oroptoelectronic circuit. The photonic or optoelectronic circuit die oncarrier is bonded using high thermally conductive material like solderor thermal epoxy to the TEC 504 and the TEC 504 in turn is mounted tothe bottom of a package made of a thermally conducting material likekovar, which in turn is mounted using solder or thermal epoxy to the hotside of the heat transfer assembly 506 (e.g., the heat pipe typeassembly). The heat pipe 506 routes heat to a place where a largesurface area component like a heat sink 510 is connected, as shown inFIGS. 5 and 6. Heat is then removed from the cold side of the heattransfer assembly 506 using air flow or convection. The laser and TECassembly are incorporated into a package like a TOSA, ROSA or otherpackage, which in turn is mounted to the heat transfer assembly 506using high thermal conducting epoxy or solder. The example in FIG. 6shows as subset of other components that may be in the optical packageincluding lenses 604, 606 and the fiber connecting assembly 614.

FIG. 7 is a perspective view of another exemplary arrangement of theheat control system 500 according to the present invention. As shown inFIG. 7, an active cooling device, shown in FIG. 7 as a TEC 504 is inthermal connection with a heat transfer assembly 506 and a circuitand/or electronic interconnect assembly 502 that can contain DC and/orRF electrical interconnections, power and ground connections orconducting planes, connections to and from the heat generating photonicor optoelectronic circuit 502 and can also contain electronic circuitsdigital and/analog and electronic discrete components, and sensingelements like thermistors. Examples of the circuit and/or electronicinterconnect assembly 502 include but are not limited to flex circuits,rigid circuits and wire bonds or other electrical bonding technique. Inthe embodiment of the heat removal system 500 of FIG. 7, the photonic oroptoelectronic circuit 502 is shown with further integration.

FIG. 8 is a perspective view of another exemplary arrangement of theheat control system 500 according to the present invention. FIG. 8 showsa heat transfer assembly in direct thermal connection to a circuit 502and flex ribbon 512 and can support directly on the heat transferassembly, patterning of various insulator layers and materials andconductor connections or direct attach of a circuit 502 or flex ribbon512 or any combination thereof. As shown in FIG. 8, the photonic oroptoelectronic circuit 502 and electronics are mounted directly to theheat transfer assembly (heat pipe type assembly) 506 greatly minimizingthe thermal impedance between the heat generating elements or elementsto be temperature stabilized and the heat transfer assembly. The ribbonor flex interconnect 512, as shown in FIG. 5 and described above, isalso mounted directly on the heat transfer assembly 506. According tothis embodiment, the heat generating sources are bonded directly to thehot side of the heat pipe type assembly removing almost all thermalresistance between the heat generating sources and the heat pipe. Theheat dissipating apparatus 510 is in thermal connection with the heattransfer assembly 506 (heat pipe type assembly) to radiate heat out ofthe heat transfer assembly 506. The advantage of this level ofintegration is that this configuration puts the heat generation sourcesright on the heat transfer assembly, making a more efficient to phasechange to the liquid inside the heat transfer assembly; and creates adifferential to transport the vapor phase of the heat transfer assemblyto the cold side of the heat transfer assembly. According to thisembodiment, the power requirement of the optical or optoelectronicdevice or subassembly incorporating this embodiment is significantlylowered, as there is no TEC and corresponding power is required tosupply the TEC.

In preferred embodiments according to the invention described herein,the heat generating components of the devices and subassembliesdescribed herein, such as photonic or optoelectronic circuits arethermally connected to the heat removal system. For example, thephotonic or optoelectronic circuits may be soldered to a thermallyconducting carrier like silicon nitride. The solder and die attach ispreferably designed to minimize the thermal resistance of the photonicor optoelectronic circuit heat generating junction to the heat removalsystem. In a more preferred embodiment, the active junction of lightemitting or detecting photonic circuits are located at the top of achip, where typically the metal interconnects are located, or the chipmay be flip chip mounted with the electronic connections mounteddirectly to electrical contacts on the carrier. Consideration must begiven to the location of the active light emitter or detector and how itis coupled off the chip, to a fiber or to a lens imaging system. Thechip carrier is then typically soldered to the heat absorbing side (hotside) of a thermo-electric cooler (TEC) that in turn has its heatrejecting side (cold side) soldered to a subassembly frame or otherthermal conducting material or component, which is then thermallyconnected to the heat transfer assembly.

In another preferred embodiment, the heat transfer assembly comprises asubstantially planar heat pipe type assembly which is a two dimensionalvessel that combines both thermal conductivity and phase transition, orother similarly performing device. The substantially planartwo-dimensional vessel is able to transport large amounts of heat due tothe latent heat evaporation being so high that the planar heat pipe typeassembly can transport much higher heat than an equivalent solidmaterial. Accordingly, a major advantage of the invention is the abilityof the devices and subassemblies described herein, which use the heattransfer assembly to transport much more heat away from the photonics,optoelectronics and electronics in the communications assembly thanstandard solid materials. A preferred example of suitable planar heatpipe type technology is a heat transfer assembly that has the desiredattributes of high thermal conductivity in a very small footprint, lowprofile, and fabricated from a material that can be connected thermallyto other materials and can act as a substrate for metallization andmounting photonic and electronic circuits. A more preferred heattransfer assembly is a titanium based flat (i.e., planar) heat pipebased on nano-structured titanium. The Ti-based heat pipe fabricationand operation is described in “A Flat Heat Pipe Architecture Based onNanostructured Titania,” Changsong Ding, Gaurav Soni, Payam Bozorgi,Brian D. Piorek, Carl D. Meinhart, and Noel C. MacDonald, Journal ofMicroelectromechanical Systems, Vol. 19, No. 4, August 2010; US PatentApp. Pub. No. US 2011/0120674 A1 (MacDonald). The Ti based planar heatpipe type assembly can be fabricated into a very low profile (e.g. lessthan 1 mm) thermal ground plane by micro welding two microfabricatedsubstrates to form the hermitically sealed vapor chamber that acts toconduct heat through the heat pipe phase change mechanism. The planarheat pipe type assembly has nano scale pillars, made of titanium oranother suitable material, that form a very high surface area and act asa hydraulic pump by wicking the liquid and greatly facilitating the heattransfer process. Using the nano scale pillar based planar heat pipetype assembly has other desirable attributes including the ability tofabricate flat shapes for integration, better performance than otherflat heat pipe materials, high fracture tolerance and lower oxidationthan copper and other heat pipe materials. An example of the titaniumbased heat pipe and its wicking structure relative to the hot and cold(heat source and heat sink respectively) are in FIG. 1 of US2011/0120674 A1. The heat pipe embodiment described for this applicationhas been shown to have an effective thermal conductivity of over 350.

Also preferably, the housing of the devices described herein compriseskovar, or another suitable material that embodies desirable propertiesfor high heat transfers, low mechanical distortion, good electrical andthermal bonding properties, can be machined or manufactured easily,enables multiple attachment processes including soldering and epoxyattach. The bottom of the housing is preferably of a suitably conductivematerial, as will be understood by those of skill in the art withreference to this disclosure.

As described herein, the advantages of the present invention include,without limitation, reduced power consumption for compact optical andoptoelectronic devices and subassemblies, smaller footprint, lower cost,and broader applications of optical, integrated optic and optoelectronictechnologies.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiments, methods, and examples herein. And, althoughthe present invention has been discussed in considerable detail withreference to certain preferred embodiments, other embodiments arepossible. Therefore, the scope of the appended claims should not belimited to the description of preferred embodiments, methods, andexamples contained herein.

What is claimed is:
 1. An optical communications apparatus, the opticalcommunications apparatus comprising: a transmitter optical subassembly;a receiver optical subassembly; a housing for enclosing the transmitteroptical subassembly and the receiver optical subassembly; an activecooling component for removing heat from at least one of one or moreheat generating components, the active cooling component including afirst direct thermal connection and a direct mechanical connection withthe at least one of one or more heat generating components; and a heattransfer assembly having a second direct thermal connection with theactive cooling component, the second direct thermal connectioncomprising a conductive platform, wherein the heat transfer assemblyprovides a mechanical supporting structure for one or more of the heatgenerating components.
 2. The optical communications apparatus of claim1, wherein the heat transfer assembly includes a substantially planartwo dimensional vessel which combines both thermal conductivity andphase transition, and wherein the conductive platform serves as a baseof the housing.
 3. The optical communications apparatus of claim 1,wherein the one or more heat generating components comprise a laser, alaser transmitter, or a non-heat generating element that requirestemperature stabilization.
 4. The optical communications apparatus ofclaim 1, wherein the one or more heat generating components comprise aphotonic integrated circuit, or an optoelectronic circuit, and theactive cooling component is in thermal connectivity with the photonicintegrated circuit or the optoelectronic circuit, and the heat transferassembly is in thermal connection with the active cooling component. 5.The optical communications apparatus of claim 1, wherein the conductiveplatform is disposed between the heat transfer assembly and the activecooling component, and the heat transfer assembly is exposed at least inpart external to the housing.
 6. The optical communications apparatus ofclaim 1, wherein the heat transfer assembly extends substantially alonga width of the housing and a length of the heat transfer assembly isexposed at least in part externally to the housing.
 7. The opticalcommunications apparatus of claim 1, wherein the heat transfer assemblyis less than 1 mm in height, and extends substantially over an area ofthe active cooling component.
 8. The optical communications apparatus ofclaim 1, wherein the heat transfer assembly is a substantially planarheat pipe type assembly comprising a two-dimensional vessel havinginterior nano-structures or micro-structures.
 9. The opticalcommunications apparatus of claim 1, wherein the one or more heatgenerating components and active cooling components are configured tostack vertically on a top of the heat transfer assembly.
 10. The opticalcommunications apparatus of claim 1, wherein the heat transfer assemblyis in direct thermal connection and direct mechanical connection with anactive heat removal element.
 11. The optical communications apparatus ofclaim 1, wherein the heat transfer assembly is in direct thermalconnection and direct mechanical connection with the active coolingcomponent, and the active cooling component is in direct thermalconnection and direct mechanical connection with the at least one of theone or more heat generating components.
 12. The optical communicationsapparatus of claim 1, wherein the optical communications apparatusfurther comprises a heat dissipating apparatus in thermal connectionwith the heat transfer assembly.